1. Field of the Invention
The present invention relates to a method of producing a composite used for an acidic gas separation film that selectively separates acidic gas from raw material gas.
2. Description of the Related Art
In recent years, a technique of selectively separating acidic gas such as carbon dioxide from raw material gas (gas to be treated) has been developed. For example, an acidic gas separation module that separates acidic gas from raw material vas using an acidic gas separation film through which acidic gas selectively permeates has been developed.
For example, JP1992-215824A (JP-H04-215824A) discloses an acidic gas separation module obtained by winding a laminate containing an acidic gas separation film around a central tube (central permeating material collection tube), in a tube wall of which through-holes are formed and which is used for collecting separated acidic gas, multiple times.
A so-called dissolution diffusion film is used for the acidic-gas separation module disclosed in JP1992-215824A (JP-H04-215824A) as an acidic gas separation film. The dissolution diffusion film separates acidic gas from raw material gas using differences in solubilities of acidic gas and materials to be separated therefrom in a film and differences in diffusibility in a film.
JP1995-102310B (JP-H07-102310B) discloses an acidic gas separation film formed with a hydrogel film that is formed by allowing a vinyl alcohol-acrylate copolymer having a cross-linked structure to absorb an aqueous solution including a carbon dioxide carrier on a carbon dioxide-permeating support, as an acidic gas separation film (carbon dioxide separation gel film) that separates carbon dioxide from raw material gas.
This acidic gas separation film is an acidic vas separation film using a so-called facilitated transport film. The facilitated transport film has a carrier reacting with acidic gas, such as a carbon dioxide carrier, therein and separates acidic gas from raw material gas by transporting the acidic gas to the opposite side of the film using the carrier.
Such an acidic gas separation film typically has a configuration in which the above-described dissolution diffusion film or facilitated transport film (hereinafter, both films are collectively referred to as a separation film) is formed on the surface of a support (porous support) having gas permeability, for example, non-woven fabric or a porous film.
For this reason, when the acidic gas separation film is formed or used, the separation layer gradually enters (infiltrates into) the porous support in some cases. Particularly, the facilitated transport film is frequently a gel film or a film having low viscosity in order to move or transport acidic vas. Accordingly, when the acidic gas separation film using the facilitated transport film is used, the separation layer gradually enters the porous support.
In the acidic gas separation film, the performance of separating out acidic gas is degraded with time due to the separation layer entering the porous support.
Further, in order for the carrier to fully function, the facilitated transport film needs to hold a large amount of water therein. For this reason, a polymer with excellent water-absorbing properties and water-holding properties is used for the facilitated transport film. In addition, the amount of water able to be absorbed of the facilitated transport film is increased and the performance of separating out acidic gas is improved when the content of the carrier such as metal carbonate is large. That is, the facilitated transport film is frequently a gel film which is extremely soft (low viscosity).
Moreover, in the acidic gas separation film using the facilitated transport film, raw material gas under the conditions of a temperature of 100° C. to 130° C. at a humidity of approximately 90% is supplied at a pressure of 1.0 MPa or greater at the time of separating out acidic gas.
Therefore, in the acidic gas separation film using the facilitated transport film, the facilitated transport film tends to enter the porous support and the durability is low.
Further, JP1987-140620A (JP-S62-140620A) discloses a method of producing an acidic gas separation film (method of producing a thin film) which includes coating a surface of a porous support with a solution including a polymer as a main component; forming a base layer formed of a polymer having air conductivity such as a silicone-based polymer; coating the base layer with an organic solvent solution including a material which becomes a separation layer as a main component; and drying the base layer to form the separation layer.
When the acidic gas separation film according to this production method has the base layer formed of a polymer having air conductivity, it is possible to form a uniform separation layer and to prevent the separation layer with low viscosity from entering the porous support.